In the preparation of strip sheet metal for subsequent use, the edges of the rolled sheet metal strips are often discarded as scrap. For example, when thin sheet metal is being slit into separate strips for use in making for example beverage cans or the like, the edges of the strip will often be wrinkled and jagged and will be unsuitable for production. Accordingly, as they leave the slitter or trimmer, the two edge strips are passed through rotary choppers which simply chop the strips up into short lengths of typically six to twelve inches which are then collected in a waste receptacle and returned to the mill as scrap.
In the past, such rotary choppers have consisted of a drum member provided, typically with two or three radially extending blades. Two such drums one above and one beneath the strip were provided, and the blades on the two drums were arranged to overlap so as to provide a shearing action on the strips. Such prior art choppers have been, generally speaking, adequate for use with the thicker gauges of strip sheet metal. However, they are found to be unsuitable for various reasons, for use with thinner gauges of sheet metal such as are now coming into wider usage for example in the manufacture of beverage cans. One of the problems of such prior art rotary choppers is the fact that no satisfactory method had been developed for continuously feeding the scrap edge strip to the chopper blades. Thus when using a thinner more flexible strip, it was possible for the scrap edge portion to become deflected so that it did not in fact reach the chopper blades, but became bent and crumpled up. This would then require shutting down the line while the crumpled portion was removed, and then restarting it again.
In addition, as the speed of the entire line was increased, the rotation of the upper and lower drums, with their blades extending outwardly from the drum surface, acted somewhat like a fan and created air currents which tended to deflect the scrap edge portions of the strip causing them to flutter or shake, so that they frequently became deflected from between the upper and lower drums, again causing a misfeed and involving shutting down the line while the crumpled or deflected scrap edge portion was cleared up.